In the microelectronic industry the prior art method of pattern replication is by means of the photolithographic process in which light of 3000 to 4000 A wavelength illuminates a photo sensitive polymer through a mask. The mask is usually constructed of clear glass with either chrome or dark emulsion patterns on it which are opaque to the light and therefore casts a shadow onto the photosensitive polymer. After exposure the polymer is subjected to a developer which removes either the exposed or unexposed areas to recreate the pattern (or its negative) of the mask. This technique has been widely used in the manufacture of microelectronic circuits because it is inexpensive and reliable and suitable for mass production. The process has the meritorious feature that it may be practiced in a clean-room atmosphere. However, this procedure has not worked well when the width of the smallest discrete element of the pattern is less than about two microns, but to the diffraction of the light used.
In an attempt to overcome this difficulty, soft x-ray lithography, as described in U.S. Pat. No. 3,743,842, Smith et al, which uses x-rays of wavelength 5-50 A greatly reduces the effects of diffraction. With this replication technique diffraction gratings with a periodicity of 3600 A have been replicated demonstrating the high resolution capability of x-ray lithography.
One disadvantage of x-ray lithography, however, in the relatively long exposure times required for replication, typically 0.1 to 10 hours using existing x-ray sources and x-ray sensitive polymers. One method of shortening the exposure time necessary for x-ray lithography is to provide a more intense source of soft x-rays, inasmuch as the exposure time is inversely proportional to the intensity of the x-ray source.